This invention relates to an audio data structure which facilities the handling of high sound-quality audio data in processing (recording, reproducing, transmitting, and constructing) the data and fulfills the high sound-quality requirement, a recording medium for the audio data structure, and an apparatus for processing its signal.
DVD video disks are optical disk on which video (moving picture) information can be recorded very densely with high quality and further various types of information, including multiangle pictures, sub-pictures, multilingual voice, and multichannel audio, can be recorded. Such DVD video disks have been developed and on the market and are finding their way into wide application. (DVD is an abbreviation for Digital Versatile Disk.)
The specifications for DVD video disks cover not only compressed multichannel audio (including AC-3 and MPEG) but also uncompressed linear PCM (including 48 kHz sampling, 16-bit quantization, 96 kHz sampling, and 24-bit quantization). The DVD video linear PCM meets the high-frequency sampling, high-number bit, high sound quality specifications, which surpass those for conventional music CDs (with 44.1 kHz sampling and 16 bit quantization). Linear PCM with 96-kHz sampling and 20- to 24-bit quantization is sufficiently qualified for the next generation digital audio disks (what is called super CDs or super audio disks).
However, the DVD video specifications have been determined by video requirements rather than audio requirements. In terms of not only sampling frequency and the number of quantization bits but also the number of recordable channels and recordable time, audio-oriented specifications surpassing the DVD video sound specifications have been expected.
To meet the expectation, DVD audio specifications have been studied (it should be noted that the DVD audio specifications have not been in the prior art yet). The DVD audio specifications have been considered to be capable of supporting linear PCM with 48- to 96-kHz sampling and 24-bit quantization employed in the DVD video specifications up to linear PCM with 192-kHz sampling and 24-bit quantization. Moreover, future versions of the DVD audio specifications might introduce much higher sound quality.
The reason why the DVD audio provides upward compatibility is that it has a part shared with DVD video that can record a large volume of data covering high-definition television images. Moreover, the DVD audio is characterized by having technical, marketable, and economical advantages in the future when it can be used as a result of advance in the DVD video.
For example, when high-capacity DVD disks to be put in practical use in future DVD video are used in DVD audio, if the recording time is constant, there is a possibility that the sampling frequency in recording, the number of quantization bits, and the number of recording channels will be increased more and more. In addition, the technique for DVD video recorders using DVD-RAMs (or rewritable DVD-RW or write-once DVD-R) to be put in practical use in the near future can be used in DVD audio recorders to come in practice soon or later.
Furthermore, as the popularization of DVD video expands its market, DVD video and DVD audio share increasingly more of the recording mediums (including DVD-ROM disks, DVD-RAM/DVD-RW disks, and DVD-R disks), unit parts (including disk drives, optical pickups, and various types of ICs), and various control programs. This accelerates the cost reduction of DVD audio products featuring high sound quality and other advantages. When DVD audio is used widely, DVD video will enjoy the future technical, marketable, and economical advantages available as a result of advance in DVD audio.
As described above, the development of DVD audio has been expected, but, as seen from the aforementioned DVD video, DVD audio with various functions and performances will possibly be proposed and developed as a result of a high-density recording disk having been developed. Specifically, there is a possibility that DVD audio with a different data structure in terms of sampling frequency, the number of quantization bits, and the number of channels will be produced. Moreover, DVD audio with a different data structure in terms of functions, such as DVD audio with or without menu images, or DVD audio with or without background images, will possibly be produced.
Accordingly, an object of the present invention is to provide a data structure that enables audio attributes to be specified track by track. The data structure makes it possible to allow the reproduction side to deal with DVD audio easily even if various functions and performances are included in the DVD audio.
The reproduction side needs a preparation time for changing the hardware devices according to the change of the attributes. The preparation time causes a break in the sound output. Accordingly, another object of the present invention is to provide a data structure which positively recognizes a break in sound and allows the designer or producer to set a sound break period arbitrary. The data structure makes it possible to make silent periods between pieces of music constant when, for example, a DVD audio disk is played back, which provides the user with a stable playback condition.
To achieve the foregoing objects, identification information to identify the type of cells by the difference in the contents of the data included in the cells is provided in cell information to specify the cells in audio contents that have cells defining at least an audio title playback unit and determines the actual playback sequence by defining the playback sequence of the cells. This enables the data structure creator side to deliberately realize data processing management, timing management, and setting management on the reproducing apparatus side during playback according to the contents of the data on the basis of the identification information.
One type of the contents of the data in the cells is for determining the length of a silent period of time. The identification information corresponding to the cell is characterized by indicating a silent cell. Providing a silent cell for determining the time of the silent period enables a silent period to be set. Using the silent period, the reproducing apparatus side can change or set the attributes. In a case where tracks with a break in sound are mingled with tracks without a break in sound, effective use of silent cells at the head of a track without a break in sound makes it possible to edit the data in such a manner that a uniform pause period giving no unnatural feeling on the whole is taken.